Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is dissolved or dispersed in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc.
In traditional dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier, such inks also generally suffer from poor water fastness and poor smear resistance. These problems can be minimized by replacing the dyes used in ink formulations with insoluble pigments. In general, pigments are superior to dyes with respect to waterfastness. However, the pigment inks tend to be unstable and settle out from the liquid vehicle over a long storage time. In addition, some pigment based inks are not as stable as expected towards pollutant. Pigment inks also have a tendency to clog the orifices of the printhead resulting in deterioration of print quality.
Accordingly, there is a need for inks with good lightfastness, stability towards pollutants, waterfastness and reliability in the printhead.
WO 00/37542 discloses the use of dendritic polymers as a pigment dispersant in water-based ink jet inks. These dendritic polymers have at least one peripheral hydrophobic long chain hydrocarbon moiety and at least one ionizable moiety. However, there is a problem with this ink using such dendritic polymer as a dispersant in that the ink has a tendency to clog the nozzles of the printhead,
It is an object of this invention to provide an ink jet ink composition that, when printed, provides an image which has improved waterfastness, lightfastness, and stability towards pollutants such as ozone. It is another object of the present invention to provide an ink jet ink composition that has improved firability through an ink jet printhead.